DAVIS — A freshman was arrested Thursday after two partially assembled pipe bombs were found in his dormitory room at UC Davis, authorities said.

More than 450 students who spent the night in dining halls or at the homes of family and friends as a precaution were allowed back to their dorms Thursday afternoon. Authorities said there was no imminent danger of explosions and no evidence of terrorism. No classes were canceled.

Police arrested 18-year-old Mark Woods, an economics major from Torrance, after questioning three other students. University spokeswoman Lisa Lapin said that Woods was cooperating with authorities. No other arrests are expected.

Woods was being held on possession of materials with the intent to make an explosive or destructive device and other charges and possession with intent to make such a device on school grounds. It was not clear if he had a lawyer.

“Police investigators say there is nothing to indicate that this case was related to a terrorist act,” a university statement said. “The investigation is continuing.”

Police became aware of the situation Wednesday night after a woman reported that students had possible explosive devices.

Two partially assembled pipe bombs were found in Woods’ dorm room, Lapin said. She said a roommate said that Woods was curious and liked to experiment but was a serious student and would have had no criminal intent.

Investigators carted off about five milk crates full of material from his room, mostly powdered substances, Lapin said.

Woods was being held Thursday at the Yolo County Jail. His bail was set at $100,000.

University officials were in the process of temporarily suspending him as a student. They will decide whether to suspend him permanently after the legal proceedings are over.

It was not clear whether Woods had retained an attorney, and a call to the Yolo County Public Defender’s Office was not returned.

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